Waves from the Big Bang: Upcoming detectors may view newborn universe

Ripples in space-time, new research shows, may soon give scientists a glimpse of the universe as it looked a tiny fraction of a second after its birth. That’s the moment when the initial runaway expansion of the universe ended in a burst of tremendous turbulence, shaking the fabric of space-time so violently that it’s reverberating faintly even today, according to some cosmological models.

UNRULY BEGINNING. These simulated peaks and troughs of energy density at the end of cosmological inflation would have spawned gravitational waves. At that time, the area represented by this graph was a trillionth of the cross-section of a proton, but with cosmic expansion, it would now be about 1 square meter. Easther, J.T. Giblin Jr., and E. Lim.

Albert Einstein predicted the existence of these waves in his general theory of relativity, which unifies time and space into a four-dimensional space-time. Gravitational effects of the birth of the universe and other extreme events can send distortions in space-time rippling outward as what scientists call gravitational waves.

Observational evidence for gravitational waves is thus far only indirect, but most physicists agree that the waves exist. “Anyone who sees a gravitational wave is going to be just enormously excited about that,” says Richard Easther of Yale University.

In recent decades, scientists have calculated the distinctive gravitational-wave patterns that would result from various phenomena, such as colliding black holes.

Now, two groups of scientists led by Easther and by Juan García-Bellido of the Independent University of Madrid have calculated the waves that would be generated by the violent end that some scientists have hypothesized for inflation—a theorized period of rapid expansion that lasted for roughly one-billion-trillion-trillionth (10–33) of a second following the Big Bang.

The teams’ calculations show that a generation of gravitational wave detectors now under development may be sensitive enough to detect these waves. If so, scientists would have a new way to confirm that inflation did occur and to measure its properties.

“This would be a direct window on that early time,” says Jolien Creighton, a physicist at the Laser Interferometer Gravitational-Wave Observatory (LIGO), a pair of linked gravitational-wave detectors operating in Hanford, Wash., and Livingston, La.

Astronomers plumb the early universe by detecting light that left a distant object long ago. Currently, the furthest back that scientists can observe is 380,000 years after the Big Bang.

Before then, the universe was so hot and dense that it was opaque to all forms of electromagnetic radiation, including visible and infrared light, radio waves, and X rays. However, gravitational waves would easily pass through this early fog and provide insight into the first moments of the Big Bang.

Easther’s and García-Bellido’s groups used different mathematical models for the end of inflation. Both teams found that if the energy density during inflation were in the lower half of the possible range, the waves produced would be detectable by an upgraded version of LIGO scheduled for completion in about 10 years. If the energy density were higher, the waves would have too high a frequency to be detectable by this observatory.

Easther’s group reports its results in an upcoming issue of the Journal of Cosmology and Astroparticle Physics. García-Bellido’s group’s calculations will appear in Physical Review Letters.

With direct observation of the universe’s first moments, scientists may learn how densely the universe was packed with energy during inflation and how inflation came to an end.

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